Technical Abstract:
Lignocellulose is a source of carbohydrates to produce many fermentation products, but pretreatment technologies that yield clean, fermentable, non-toxic sugar hydrolysates are still needed. We have developed a novel process that results in hemicellulose hydrolysates essentially free of toxic degradation products while yielding wood fibers useful for paper production. The pulp and paper industry has an existing infrastructure that could become the basis for a large-scale biorefining industry. We describe here a value-prior-to-pulping approach that generates a readily-fermentable hemicellulose-derived sugar stream from a pretreatment of wood chips. Diethyl oxalate (DEO) is a liquid that will vaporize quickly at elevated temperatures, infiltrate the wood chip, and hydrolyze to oxalic acid. This vapor-phase process uses only the water present in the wood chip for hydrolysis. Hemicellulosic sugars can be removed in a counter-current washing process. Cellulose in the resulting chips is largely unaffected by the pretreatment conditions, and the fibers can be used to produce pulp. The extent of carbohydrate removal can be adjusted by chemical loading, hydrolysis temperature, or length of treatment. Pretreatment of chips for thermomechanical pulp decreases electrical refiner energy and produces a stronger pulp. Pretreatment for chemical pulps creates an improved wood chip with more extensive lignin removal for the same cooking conditions. The hemicellulose hydrolysate is a mixture of mono and oligosaccharides that can be readily fermented with Escherichia coli, Saccharomyces cerevisiae, and Pichia stipitis. Increasing the pretreatment intensity improves the ability of rumen microorganisms to degrade the residual wood, indicating utility for total saccharification and fermentation.